Virtually every electronic device includes one or more varieties of printed circuit boards (PCBs). PCBs are relatively thin, layered substrates upon which integrated circuits and other electronic components are attached. A printed circuit board typically includes a plurality of electrically conductive and insulating layers arranged in a sandwich-like fashion. Conductive layers generally have conductive paths or traces, isolated from one another by the insulating material of the insulating layers, and routed within a plane. These traces are generally designed to electrically contact conductive portions of the electronic components mounted on the PCB, forming electrical interconnects. Insulating layers electrically isolate these conductive paths from one another. The principle structure of conductive traces and layers of insulating material is also used on a smaller scale within a packaged microchip having a PCB-like package substrate.
In order to make connection between two or more conductive layers of a PCB, or in order to make connection between an electrical component mounted on the PCB, a plated through hole connection is used. Plated through hole connections are formed by drilling through two or more layers of the PCB in a direction normal to the major surface of the PCB. This drilling action leaves a vacant cavity or barrel, the periphery of which is coated with conductive material to form an electrical connection between conductive layers along the cavity. In addition to providing a electrical connection between conductive layers of the PCB, the plated through hole connections offer a greater degree of planarity and mechanical stability to PCBs.
One disadvantage of plated through hole connections, however, is their behavior when conducting high frequency signals. Basically, as the frequency of the signal traveling through the plated through hole connection increases, the resistance of the plated through hole connection increases. Since the overall trend in the electronics industry usually involves increasing the speed (or frequency) at which the various electronics devices operate, the high frequency disadvantages of plated through hole connections become more and more pronounced with each generation of electronic devices.